'02 4.7 4wd. Hey guys. When started cold my D idles up and down from 1,500 rpms down to around 650. It goes away as she warms up but that's not all. When fully warm she'll occaisionally fluctuate between 500 and 1,300.

There seems to be no pattern. Just out of nowhere she'll start doing this, sometimes quickly and sometimes the tach will sit still around 850-900.

New IAC and throttle body cleaned, new cam sensor, crank sensor, ecm, ign switch.

No vac leaks as far as I can tell. No engine light or codes at all.

Any ideas? I'm pretty stumped.

 

did you change the tps yet??? very common cause of idle fluctuation

 

+1 on TPS, but another one is the power steering pressure switch on the high pressure line by the pump. It monitors engine speed & steering pressure to prevent it from stalling when turning tightly.

Bob

 

Thanks guys. I went ahead and replaced the TPS
a it knocked the problem right out. I'm gonna check out the steering switch stated above and probably replace it too. I might as well since everything else is new now (except plugs, coming soon).

Thanks again.